FIG. 1 illustrates a block diagram of a transceiver module 2 currently used in optical communications. The transceiver module 2 includes a transmitter portion 3 a receiver portion 4. The transmitter and receiver portions 3 and 4 are controlled by a transceiver controller 6. The transmitter portion 3 comprises components for transmitting data in the form of amplitude modulated optical signals over multiple fibers (not shown). The transmitter portion includes a laser driver 11 and a plurality of laser diodes 12. The laser driver 11 outputs electrical signals to the laser diodes 12 to modulate the laser diodes 12, thereby causing them to output optical signals that have power levels corresponding to logic 1s and logic 0s. An optics system (not shown) of the transceiver module 2 focuses the coherent light beams produced by the laser diodes 12 into the ends of respective transmit optical fibers (not shown) held within a connector (not shown) that mates with the transceiver module.
A plurality of monitor photodiodes 14 monitor the output power levels of the respective laser diodes 12 and produce respective electrical analog feedback signals that are delivered to an analog-to-digital converter (ADC) 15, which converts that electrical analog signals into digital signals. The digital signals are input to the transceiver controller 6, which processes them to obtain respective average output power levels for the respective laser diodes 12. The controller 6 outputs controls signals to the laser driver 11 to cause it to adjust the respective bias current signals output to the respective laser diodes 12 such that the average output power levels of the laser diodes are maintained at relatively constant levels.
The receiver portion 4 includes a plurality of receive photodiodes 21 that receive incoming optical signals output from the ends of respective receive optical fibers (not shown) held in the connector referred to above that mates with the transceiver module. An optics system (not shown) of the receiver portion 4 focuses the light output from the ends of the receive optical fibers onto the respective receive photodiodes 21. The connector may include an optics system that focuses light from the ends of the receive fibers onto the optics system of the receive portion of the transceiver module, which then focuses the light onto the photodiodes. The receive photodiodes 21 convert the incoming optical signals into electrical analog signals. An ADC 22 converts the electrical analog signals into electrical digital signals suitable for processing by the transceiver controller 6. The transceiver controller 6 processes the digital signals to recover the data represented by the signals.
FIG. 2A illustrates a perspective view of a known multi-fiber connector module 31 designed for use with a transceiver module of the type described above with reference to FIG. 1. This connector module 31 is manufacture by US Conec Ltd. of Hickory, N.C. and has become known in the optical fiber connector industry as the MTP® connector. The connector module 31 holds ends of the transmit and receive fibers and has an optics system that couples light from the laser diodes 12 into the ends of transmit fibers and from the ends of the receive fibers onto the photodiodes 21. The connector module 31 receives a duplex fiber ribbon (transmit and receive fibers) 32 having a total of 4, 8, 12 or 24 optical fibers. A strain relief device 33 holds the fibers grips the fibers below the ends to prevent the fiber ends from moving in the event that mechanical loading on the cable occurs due to tugging or pulling of the cable. This prevents the integrity of the optical signals from being degraded due to a problem referred to in the optical communications industry as “wiggle” or “wiggle losses”.
The connector module 31 has an outer housing 34 and an inner housing 35. The inner housing has latching elements 36 thereon for securing the module 31 to a receptacle 61 of a transceiver module. A collar 31 surrounds the outer housing 34 of the connector module 31 and prevents the latching elements 36A and 36B from unlatching when the connector module 31 is connected to the transceiver module receptacle 61. The ends of the transmit and receive fibers are held within a multi-fiber ferrule 37 that extends slightly beyond the end 38 of the inner housing 35. The ends (not shown) of the fibers are polished and extend a very small distance beyond the end of the ferrule 38 such that the polished end of each fiber provides a flat optical element for coupling light between the polished end and an optical element (not shown) of the receptacle 61.
FIG. 2B illustrates a cutaway view of the MTP connector module 31 shown in FIG. 2A that reveals features inside of the connector module 31 and receptacle 61. Inside of the inner housing 35, the ferrule 37 is moveably secured and spring-loaded to allow it to move in the axial direction of the fibers. A spring (not shown) is located in the cylindrical groove 42 formed in the inner housing 35 of the connector module 31. When the connector module 31 is latched to the receptacle 61, the outer end 37A of the ferrule 37 is in abutment with the contact surface (not shown) of the receptacle 61. This contact surface of the receptacle 61 contains optical elements (not shown), which will be described below in more detail with reference to FIG. 2C. The abutment of the ferrule end 37A with this contact surface of the receptacle 61 exerts a force on the end 37A of the ferrule 37 in the axial direction of the fibers that causes the end 37B of the ferrule to press against and thereby compress the spring to allow the ferrule 37 to retract into the inner housing 35 of the connector module 31. The ferrule 37 retracts until the ferrule end 37A is flush with the end 38 of the inner housing 35. This abutment of the ferrule end 37A against the contact surface of the receptacle 61 ensures that the flat optical elements comprising the polished ends of the fibers are in contact with the optics elements contained in the contact surface, which ensures efficient optical coupling.
FIG. 2C illustrates a cutaway view of the MTP connector module 31 shown in FIG. 2B with the connector module 31 connected to the receptacle 61. Only one side of the ferrule 37 is shown in FIG. 2C. The ferrule 37 has a cylindrical opening 37C formed in the left side thereof and a cylindrical opening (not shown) formed in the right side thereof for receiving cylindrical pins 62A and 62B that extend from the contact surface 63 of the receptacle 61 for guiding and alignment. The fibers (not shown) are positioned in respective grooves 41 formed in the ferrule 37 and secured thereto by an adhesive material. Latching elements 64A and 64B of the receptacle 61 engage latching elements 36A and 36B to lock the connector module 31 to the receptacle 61. The collar 31 is in sliding engagement with the outer housing of the connector module 31 and has an inner surface 39 that presses against the latching elements 64A and 64B to prevent them from disengaging from the latching elements 36A and 36B. This tight physical coupling and precision alignment of the connector module 31 and the receptacle 61 results in tight optical alignment, which, in turn, results in low optical losses and good signal integrity.
The MTP connector module 31 has been widely adopted due to its low wiggle loss, high optical coupling efficiency and high manufacturing yield. One of the disadvantages of the MTP connector module 31 is that it is relatively expensive due to the fact that the ends of the fibers must be polished and due to the fact that the parts must be manufactured with extremely high precision in order to achieve precise physical and optical alignment. Because of the precision with which physical alignment must be maintained in order to achieve the necessary optical coupling efficiency, any reduction in part precision will result in unacceptable optical losses. Attempts have been made to use cleaved fiber ends in the MTP connector module, but such attempts generally have been unsuccessful because they result in the connector modules having inconsistent optical coupling losses.
A multi-fiber connector known in the optical fiber connector industry as the PT connector module that uses cleaved fiber ends has been proposed. In the proposed PT connector module, the cleaved ends of the fibers are guided into V-grooves formed in the connector module and secured therein with a refractive index matching epoxy. FIG. 3 illustrates the optical path taken by light output from a VCSEL laser 71 of the transceiver module (not shown) as the light passes through the transceiver receptacle and is focused onto the end of a transmit fiber in the PT connector module. The light passes through a conventional lens 72 of the transceiver module, which produces a focused beam of light that is folded by a folding mirror 73 of the connector module such that the focal point of the focused beam coincides with the end 74 of a transmit fiber 75.
Although the PT connector module has a reduced cost associated with using cleaved fibers instead of polished fibers, like the MTP connector module, the parts of the PTC connector module must be made with extremely high precision in order to ensure low wiggle loss and low optical loss due to other factors, such as parts moving by unequal amounts as the temperature varies due to differences in the coefficients of thermal expansion (CTE) of the various parts. This movement can cause optical misalignment, which results in optical losses along the optical path.
It would be desirable to provide a multi-fiber connector module that can be made with reduced cost by using cleaved fibers instead of polished fibers and that can be made with less expensive parts without sacrificing performance or manufacturing yield.